The present invention relates to laminated three-layer resinoid wheels having a core layer of reinforcing material for cutting hard metal materials and a method for producing the same.
Reinforced resinoid wheels are known which comprise a core layer of reinforcing material such as glass cloth, glass mat or glass fiber net and outer layers covering the opposite surfaces of the core layer. With the conventional method of production, however, it is difficult to position the core layer at the center of thickness of the abrasive wheel, with the result that the core layer is formed as deviated toward one side. Consequently, the abrasive wheel is brought out of balance during operation and is prone to distortion and cracking. To describe in detail, conventional three-layer resinoid wheels of the type described are produced by placing a kneaded resinoid abrasive composition into a die of a given shape, smoothing the surface of the composition with raking means to give a uniform thickness to the mass of the composition, placing a sheet of reinforcing material over the composition, superposing another raked layer of the abrasive composition over the reinforcing sheet and subjecting the mass of layers to compression molding. However, this method has the drawback that relatively coarse abrasive grains are caught by the raking means and brought to the surface, rendering the uncured abrasive material in the mold coarser in its front surface and finer in its rear surface to result in uneven grain size distribution. Furthermore, since the raked mass of the starting abrasive composition is subjected to compression molding by being pressed on one side, there arises a difference between the pressures acting on the upper and lower surfaces of the mass. Consequently, the grinding wheel obtained becomes uneven in hardness, inasmuch as the product has high hardness where many coarse abrasive grains are present but low hardness where smaller grains are predominant. When put to use, the grinding wheel wears away more markedly where it contains many fine abrasive grains than where coarse grains predominate, so that an uneven wear takes place. As a result, the grinding wheel not only fails to cut a work straight but is possibly broken. Moreover, if the abrasive composition is not fully raked, the resulting product will have a nonuniform thickness, consequently producing errors when cutting a hard metal material, and the product is broken when it is markedly irregular in thickness.